Micro-valves are used to dispense small amounts of fluid, typically in the range of 1 nl to 1 ml. Accurately knowing the volume of liquid that has been dispensed is important in various industries, such as the pharmaceutical industry, the production of ink-jet printers and in various nanotechnology applications, including but not limited to 3D cell printing. In these applications, the fluid being dispensed is often high value, and it is often necessary to repeatedly perform the same dispensing operation many times. As a result, it is important for micro-valves to be able to dispense precisely, accurately and quickly.
Conventional micro-valves have used solenoid and spring actuation methods. A solenoid with an ancillary electromagnetic coil fitted can be used to induce a magnetic field by inducing an electromagnetic field around both a floating, or unfixed, armature and a fixed armature within the valve, causing them to attract each other—this is the same effect as two magnets being attracted together. This causes the floating armature to move, and thus to open the valve. Thereafter, when the solenoid is switched off by turning off the electrical current, the magnetic field is released. A spring, that was compressed during the opening of the valve, is then used to return the floating armature to its original position and thus close the valve.
However, this arrangement can lead to turbulence within the valve. The floating armature is typically positioned within the fluid path through the valve, thereby at least partially obstructing the fluid flow. The irregular shape of the floating armature (often a cylinder with portions sliced away from opposite sides) can lead to turbulence being induced within the micro-valve, which can lead to inaccurate dispensing. Such irregular shapes can have the effect, when an electromagnetic induced field is applied, to randomly rotate such an armature each and every time it is switched on and off, such random rotation will create fluid turbulence. Also, the spring is conventionally positioned within the direct fluid path. Once again, the spring can act as an obstacle in the fluid path and thus introduce turbulence. This can be especially problematic because the spring is conventionally in the valve head, near the valve outlet, and so the induced turbulence is not dissipated before the fluid reaches the outlet.
The present invention aims to at least partially solve these problems by providing an alternative micro-valve construction.
US 2009/0121541 discloses a solenoid valve for a brake system. U.S. Pat. No. 5,704,587 discloses an electromagnetic valve device. Both are examples of the systems discussed above, in which a spring for opening a valve is within the direct fluid path, between the floating armature and the valve outlet.
US 2007/0291581 discloses a micromixer. A spring is used to adjust the pressure difference required to actuate a plunger in the disclosed micromixer. The micromixer operates in a significantly different manner to microvalve. The force to overcome the spring is provided by a pressure difference within the bores of the micromixer, rather than by electromagnetism.